When I'm working with VA-X in VS 6.0, making a text selection sometimes results in sudden disappearing of enhanced syntax colouring in source editor. Other features still work. Only restarting of VS helps then.
MJV discovered that going to tools-options and cancel restores the coloring as long as nothing is highlighted. This is very annoying. I hoped that it would be fixed in 1225.
I've been able to keep the color from disappearing based on the IDE settings for Text Foreground and Background colors. I have them set to Automatic and Light Gray. It seems that if I had them explicitly set to say White and Black I'd have the same problems you incurred. Changing them to say White/Lt. Gray made things better, however the color disappears for other reasons (see link). Leaving the foreground Automatic and the Background Light Gray worked best for me.